Nebulizers, or atomizers as they are sometimes called, are devices that generate a fine spray or aerosol from a liquid. A particularly useful application for nebulizers is to provide a fine spray containing a dissolved or a suspended particulate drug for administration to a patient by inhalation.
Piezo-mesh based nebulizers are commonly used to generate aerosols in such drug delivery apparatus, whereby for instance a piezoelectric element vibrates a nozzle plate (also referred to as a mesh) to produce the fine aerosol spray. In some nebulizers the piezoelectric element is bonded to, or otherwise in contact with, a nozzle plate element, whereas in other nebulizers the nozzle plate element is separate from (i.e. not in contact with) the piezoelectric element.
The rate at which the liquid is atomized is affected by the operation and design of the nebulizer and also by the properties of the liquid. In some types of nebulizers (for example pneumatic jet-type nebulizers), the rate can be known for a particular combination of nebulizer and medication, and it is possible to estimate a dosage of medication delivered to a patient based on the total time that the aerosol is generated and inhaled by the patient.
However, in nebulizers that use a mesh to nebulize the liquid, the rate or amount of droplets produced varies over time as the holes in the mesh become blocked. This means that it is not possible to calculate the dosage delivered to the patient in the same way as for pneumatic jet-type nebulizers. Instead, in piezo-mesh nebulizers a volumetric metering method may be used to make sure that the correct dose is provided to the patient. In particular, prior to use with a particular medication, the nebulizer is fitted with a metering chamber that holds only the required volume of medication for a single dose. Such volumetric metering methods are described in EP 1465692.
Medication for use in nebulizers may be supplied in a range of containers or vials and are typically supplied to the patient in quantities sufficient for treatment over a number of days (e.g. 30). The amount of medication to be delivered during each use of the nebulizer (dosage) can be set by making use of a data carrier that is associated with the medication container or vial and that contains specific treatment information that is read by the nebulizer prior to use. The data carrier can also be used to store details of each completed dose or treatment (e.g. the proportion of the dose delivered to the patient and the type of medication administered).
This data can subsequently be uploaded to a computer for analysis using suitable software, and this allows a healthcare professional to monitor that the patient is correctly using the device and undergoing the prescribed treatment.
Typically, prior to use of the nebulizer, a patient is required to fit an appropriately sized metering chamber into the nebulizer and pour the required medication from a vial into the metering chamber. Once the medication has been poured in, the nebulizer can read the data carrier associated with the medication (and also any data carrier associated with the metering chamber) and set its operating parameters accordingly.
However, a single nebulizer can be used with a range of different liquid medications, and patients are often prescribed more than one type of drug at a time. Although the use of a data carrier on the metering chamber allows the fitting of the correct metering chamber to be determined, and the nebulizer can read the data carrier associated with the medication packaging, there is currently no way of verifying that the correct medication has been poured into the nebulizer.
The loading of the wrong medication into the nebulizer can cause a number of problems. In particular, some protein drugs, such as Dinase and A1 AT, can be damaged if they are contaminated with other drug substances, but more importantly, if the wrong medication is loaded into a metering chamber that is for use with another medication, the wrong dosage (or even an inappropriate liquid) could be administered to the patient. For example, colistimethate sodium may have an inhaled dose size of 0.3 ml and hypertonic saline may have an inhaled dose size of 1.0 ml—and therefore mixing up the medications will result in the wrong dosage being given to the patient when the nebulizer is used).
Therefore, there is a need for a technique to check or verify that the correct liquid (medication) has been dispensed by a nebulizer.